This invention relates to a transportation system and specifically to an apparatus which supplies a vehicle command signal operatively decelerating the vehicle to a selected landing at which a stop is to be made.
Many types of command signals have been utilized within motor control circuits for comparison with signals which represent the actual operation of the motor and the objects they control to develop an error signal controlling the energization of the motor. Such closed loop control systems have sensed various facets of the operation to develop operational responsive signals such as, for example, the position of the motor drive shaft or of the object it controls, the speed of the drive shaft rotation or the object it controls, or the counter-electromotive force (CEMF) sensed at the motor armature circuit. In many prior closed loop control systems, the absence of an error signal has indicated that the motor is operating in accordance with the motor command signal which is thus equal to the magnitude of the motor responsive signal. A difference existing between the command and operational responsive signals indicates that the commanded object is either operating too fast or too slow or is not at a proper position and thus an error signal is developed to correspondingly speed up or slow down the drive motor.
Some motor control systems designed for general industrial applications have provided selectively variable closed looped circuits for providing a selectively variable time rate command signal which is combined with a motor responsive signal for providing a motor controlling error signal to accelerate and decelerate the motor as well as operate the motor at a constant speed. One such system has selectively operated a switching comparator for supplying a signal which is integrated in accordance with a preselected rate by an integrating circuit for providing the motor command signal coupled for developing the error signal and further coupled through an inverting circuit to be selectively combined with a run command signal at a summing circuit operatively connected for controlling the operation of the comparator and thus the running and stopping of the motor. While such a system has been highly desirable for controlling D.C. motors used in steel mill process applications, it has not provided the smooth decelerating characteristic desired for passenger comfort in guiding a transport vehicle to a selected landing, such as in an elevator system.
Some prior transportation systems have formulated a vehicle command signal directly in response to a signal received from a tachometer for decelerating a vehicle, such as shown in the U.S. Pat. No. 3,631,326 issued on Dec. 28, 1971. Furthermore, some systems, such as illustrated in the U.S. Pat. No. 3,631,326, provide an acceleration command signal which is compared to a sensed acceleration signal to develop an acceleration error signal to control the energization of an elevator motive means and thus the vehicle movement.